This invention relates to a device or apparatus for manipulating matter within a confined or inaccessible space, especially during surgery in a living body.
Matter may be manipulated in such circumstances in various ways, for example by application of a ligature, by suturing, by cutting with a knife or by cutting or grasping with elongate elements moving in a scissors action, or by capture and retrieval in devices such as screens, baskets, barriers, pouches, or retractors. Such manipulation may be difficult when operating in the confined space of a very deep wound or through a small arthroscopic or other endoscopic incision or body aperture.
Many forms of apparatus for performing surgical operations have been proposed previously using resilient steel wires which spring apart when extended from the distal end of a tube and which can be brought together again on withdrawal back into the tube. Examples of such known devices may be seen in U.S. Pat. Nos. 2,114,695, 2,137,710, 2,670,519, 3,404,677, 4,174,715, 4,190,042, 4,222,380, 4,249,533, 4,347,846, 4,655,219, 4,691,705, 4,741,335, 4,768,505 and 4,909,789. However, these devices may not be completely satisfactory for various reasons, especially after repeated use or long storage which may fatigue the materials used.
Attempts have been made to use heat recoverable shape memory metals in surgical apparatus, but these suffer from inconvenience and from the risk of damage to living tissues resulting from the need either to cool the memory metal while positioning it in the body so that body heat thereafter actuates the shape memory effect, or to heat the metal above body temperature to actuate it after positioning. Examples of such attempts are described in U.S. Pat. Nos. 4,509,517, 3,868,956 and 4,425,908.
U.S. Pat. No. 4,935,068 to Duerig, which is commonly assigned with the present application and whose teaching and disclosure are incorporated herein by reference, describes the fundamental principles of shape memory alloys. Some alloys which are capable of transforming between artensitic and austenitic phases exhibit a shape memory effect. The transformation between phases may be caused by a change in temperature. For example, a shape memory alloy in the martensitic phase will begin to transform to the austenitic phase when its temperature rises above the austenite start temperature, A.sub.s, and the transformation will be complete when the temperature rises above the austenite finish temperature, A.sub.f. The forward transformation will begin when the temperature drops below the martensite start temperature, M.sub.s, and will be complete when the temperature drops below the martensite finish temperature, M.sub.f. The temperatures M.sub.s, M.sub.f, A.sub.s, and A.sub.f define the thermal transformation hysteresis loop of the shape memory alloy.
Under certain conditions, shape memory alloys exhibit pseudoelasticity, which does not rely on temperature change in order to accomplish shape change. A pseudoelastic alloy is capable of being elastically deformed far beyond the elastic limits of conventional metals.
The property of pseudoelasticity of certain shape memory alloys, which preferably is used in the devices of this invention, is the subject of a paper entitled "An Engineer's Perspective of Pseudoelasticity", by T. W. Duerig and R. Zadno, published in Engineering Aspects of Shape Memory Alloys, page 380, T. W. Duerig, K. Melton, D. Stoeckel, and M. Wayman, editors, Butterworth Publishers, 1990 (proceedings of a conference entitled "Engineering Aspects of Shape Memory Alloys", held in Lansing, Mich. in August 1988). As discussed in the paper, the disclosure of which is incorporated herein by reference, certain alloys are capable of exhibiting pseudoelasticity of two types.
A first type of pseudoelasticity, "superelasticity" (also sometimes referred to as non-linear pseudoelasticity) arises in appropriately treated alloys while they are in their austenitic phase at a temperature which is greater than A.sub.s and less than M.sub.d (M.sub.d is the maximum temperature at which the transformation to the martensitic phase can be induced by the application of stress). Superelasticity can be achieved when the alloy is annealed at a temperature which is less than the temperature at which the alloy is fully recrystallized. Alternative methods of creating superelasticity in shape memory alloys, such as solution treating and ageing, or alloying, are also discussed in "An Engineer's Perspective of Pseudoelasticity", referenced above. An article may be provided with a desired configuration by holding it in that configuration during annealing, or during solution treatment and ageing. An article formed from an alloy which exhibits superelasticity can be deformed substantially reversibly up to 11% or even more.
A second type of pseudoelasticity, is "linear pseudoelasticity". In contrast to superelasticity, "linear pseudoelasticity", is believed not to be accompanied by a phase change. It is exhibited by shape memory alloys which have been cold worked in the martensitic phase, but have not been annealed in the manner discussed above for superelastic behaviour. An article formed from an alloy which exhibits linear pseudoelasticity can be deformed substantially reversibly by 4% or even more. The treatment of shape memory alloys to enhance their pseudoelastic properties is also discussed in above-mentioned U.S. Pat. No. 4,935,068 to Duerig, the entire disclosure of which is incorporated herein by reference.
Certain aspects of the present invention use, or prefer to use, pseudoelastic materials (or in some cases superelastic materials) which bend pseudoelastically (or superelastically in the case of superelastic materials) to perform manipulations which may be difficult or impossible to achieve reliably with previously known devices. Pseudoelastic alloys have previously been described for various non-manipulative devices such as lesion marker probes, bone anchors, heart valves, intrauterine devices, dental arch wire, coil stents and filters, as described in U.S. Pat. Nos. 4,665,906 (Jervis), 4,616,656 (Nicholson), 4,898,156 (Gatturna), 4,899,743 (Nicholson), and 4,946,468 (Li). In one case, U.S. Pat. No. 4,926,860 (Stice) describes a straight suturing needle made of such alloy which ensures the needle emerges straight after being inserted through a curved cannula. None of these known uses in any way suggests the present ingenious use of the power of pseudoelastic bending on extending a pseudoelastic manipulator means from a cannula to perform manipulations in difficult locations.
Certain aspects and embodiments of the present invention provide new devices and apparatuses or new configurations of device and apparatus, using elastic materials, for manipulating matter within a confined or inaccessible space. Preferred aspects and embodiments of the present invention provide devices and apparatuses for manipulating matter within a confided or inaccessible space using pseudoelastic materials which bend pseudoelastically to perform manipulations which may be difficult or impossible to achieve reliably with previously known devices. Other aspects and embodiments of the present invention provide devices and apparatuses for manipulating matter within a confined or inaccessible space using superelastic materials which bend superelastically to perform manipulations which may be difficult or impossible to achieve reliably with previously known devices.
Where it appears in relation to any aspect of the invention, the term "elastic material" is used herein to mean a material that has been designed such that it is capable of being deformed by an applied stress and then recoves to or toward its original unstressed shape or configuration when the stress is removed. The elastic material preferred in certain aspects of the invention, and required in other aspects of the invention is preferably visibly elastic.
The property of elasticity is shared by all solids but with vastly differing characteristics and for different underlying reasons. A rubber band is common and visible example of an elastic material. If the stretching and recovery of a rubber band is quantified by converting force and deflection to stress and strain, one finds that a stress of several thousand pounds per square inch causes several hundred per cent strain. If the stress is divided by the accompanying strain the result in called the elastic modulus. For rubber the modulus is about 1000 pounds per square inch, psi. The path of strain versus stress during stretching and relaxing can be seen to be non-linear, Curve A in Figure X.
Hard, brittle materials such as glass are at the other extreme of the elastic spectrum. Tensile stress causes slight elongation and stress versus strain is a linear relation for loading and unloading, see curve B, Figure X. If the stress rises high enough to break the test piece, material adjacent to the fracture shows no set or plastic deformation.
Common alloys for construction such steel or brass have elastic moduli slightly greater than glass. As with glass, stress and strain are linear at low strain levels. What makes these materials different from glass is that the linear elastic range is followed by a region of plastic deformation. As the stress exceeds the elastic limit, the alloys flow with progressive stress increases. If the stress is returned to zero, these alloys recover elastically, . . . but with a permanent set equal to the plastic flow, see Curve C, Figure X. That a small cross section of these materials can support a relatively heavy load and that an overload causes plastic deformation rather than brittle failure is what makes them so useful for construction. Normal practice restricts design stress to be only a fraction of the linear stress versus strain range. This is because repeated excursions into the plastic flow range causes a build up of defects in the alloy structure which leads to fatigue failure.
The pseudo-elastic alloys fit between rubber and structural alloys in this spectrum. The linear pseudoelastic alloys are depicted by Curve D in Figure X. These alloys have a loading and unloading characteristic similar to that of rubber but at much higher stress and much lower strain.
At low stresses, those pseudoelastic materials designated as superelastic alloys have linear loading-unloading characteristics like glass or structural alloys. As the stress becomes high enough to induce the austenitic phase to transform to martensite, then a plateau is reached where only slightly increasing stress cause high elongation. At the end of the plateau, stress and strain are linear with a modulus of elasticity similar to the low-strain region. Upon unloading, superelastic alloys retrace the plateau, but at a lower stress, see Curve E, Figure X.
Pseudoelasticity was first reported in the intermetallic compound gold-cadmium in 1932. Olander, the crystallographer who made the observation, described the material as rubber-like (J. Am. Chem Soc., 54, 3819, 1932) Even though the pseudoelastic alloys have less than one tenth the elastic range of a rubber band, they have nearly ten times the elastic range found in the best standard spring alloys (one percent elasticity).
Designers are offered the combination of relatively high load bearing capacity and large strain range without huge stresses and with exceptionally great fatigue life relative to the strain. Pseudoelastic alloys truly are rubber-like structural alloys.
In the context of this patent, the term "elastic" is used to describe those members which are designed to display the visibly elastic deformation of rubber. Pseudoelasticity is the preferred basis for this dramatic behavior, however, elastomers and thin sections of standard spring materials in bend or torque can also be useful.
Those members which are designed to be rigid within the scope of this patent are acknowledged to be elastic, but not visibly elastic.
The visibly elastic material in this patent can be polymeric or metallic, or a combination of both. For certain embodiments the use of alloys is preferred. Alloys that exhibit pseudoelasticity, in particular superelasticity, are preferred for certain aspects of the invention and required for other aspects of the invention. Preferred elastic materials exhibit greater than 1% elastic deformation, more generally greater than 2% elastic deformation. Preferably, the elastic materials exhibit greater than 4% elastic deformation, more preferably greater than 6% elastic deformation.
In certain aspects of the invention, and preferably in other aspects of the invention, an elastic member is used that is at least partially formed from a pseudoelastic material, such as a shape memory alloy that exhibits pseudoelasticity. Alloys which exhibit superelasticity (also referred to in the literature as non-linear pseudoelasticity), are especially preferred, eg shape memory alloys which exhibit superelasticity.
While the alloy that is used in the devices of various aspects of the invention, or in preferred embodiments of other aspects of the invention may exhibit either linear pseudoelasticity or superelasticity (which is sometimes referred to as non-linear pseudoelasticity), or pseudoelasticity of an intermediate type, it may also be preferred that it exhibit superelasticity because of the large amount of deformation that is available with superelasticity without the onset of plastic deformation. U.S. Pat. No. 4,665,906 to Jervis, which is commonly assigned with the present application and whose teaching and disclosure is incorporated herein by reference, describes the use of pseudoelastic shape memory alloys in medical devices.
Where a pseudoelastic material is used, it will be selected according to the characteristics desired of the article. One preferred material is a nickel titanium based alloy, which may include additional elements which might affect the yield strength that is available from the alloy or the temperature at which particular desired pseudoelastic characteristics are obtained. For example, the alloy may be a binary alloy consisting essentially of nickel and titanium, for example 50.8 atomic percent nickel and 49.2 atomic percent titanium, or it may include a quantity of a third element such as copper, cobalt, vanadium, chromium or iron. Alloys consisting essentially of nickel, titanium and vanadium, such as disclosed in U.S. Pat. No. 4,505,767, the disclosure of which is incorporated herein by reference, are preferred for some applications, particularly since they can also exhibit superelastic properties at or around body temperatures, and because they are stiffer and/or can store more elastic energy. Copper based alloys may also be used, for example alloys consisting essentially of copper, aluminium and nickel; copper, aluminium and zinc; and copper and zinc.
An article exhibiting superelasticity can be substantially reversibly deformed, by as much as eight percent or more. For example, a 1.00 meter length of superelastic wire may be stretched to 1.08 meters in length, wherein its alloy will undergo a phase change to at least a partially more martensitic phase known as stress-induced-martensite. Upon release of the stress, the wire will return substantially to its 1.00 meter length, and its alloy will, correspondingly, return at least substantially toward its more austenitic phase. By way of contrast, a similar wire of spring steel or other conventional metal may only be elastically stretched to a maximum of approximately one percent, or to 1.01 meter in length, depending on the metal. Any further stretching of the conventional wire, if not resulting in actual breakage of the wire, will result in a non-elastic (plastic) transformation such that, upon release of the stress, the wire will not return to its original length. Linear pseudoelastic and superelastic materials may also be bent, twisted, and compressed, rather than stretched, to a far greater degree than conventional metals.
It is believed that the superelastic property is achieved by phase transformation within the alloy, rather than by the dislocation movements which occur during the plastic deformation of ordinary metals. A superelastic material may be deformed and released thousands of times,